1. Field of the Invention
This disclosure relates to a backlight unit, and more particularly to a backlight unit adapted to implement enhanced light efficiency and uniform brightness, and a liquid crystal display device having the same.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices are widening their application fields as a result of their features, such as their light weight, slimness, low driving voltage, and so on. This trend is evident in the ways in which the LCD devices have been applied to office automation equipment, audio equipment, video equipment, and more. The LCD device controls a transmitting amount of light on the basis of image signals applied to a plurality of control switches, in order to display a picture.
The LCD device, which is not self-luminescent, includes a backlight unit irradiating light on the rear surface of an LCD panel in which a picture is displayed. The backlight unit is classified as either an edge type or a direct type in accordance with the disposition of its light source.
The edge type backlight unit includes a light source which is disposed in a position corresponding to a side of the LCD panel. Also, the edge type backlight unit irradiates light emitted from the light source onto the entire surface of the LCD panel using a light guide panel. On the other hand, the direct type backlight unit includes a plurality of light sources arranged opposite the rear surface of the LCD panel. These plural light sources directly apply light to the rear surface of the LCD panel. The direct type backlight unit has a higher brightness and a wider luminescent surface than the edge type backlight unit because it employs a plurality of light sources. In addition, the backlight unit becomes larger in size corresponding to the increased size of the LCD device. In view of these points, direct type backlight units are widely used in LCD devices.
Such a direct type backlight unit generates a difference in brightness between the regions that include a light source and those that do not. This results from the configuration in which plural light sources are arranged at fixed intervals on the rear surface of the LCD panel. In other words, it is difficult for the direct type backlight unit to implement uniform brightness.
To address this problem, a direct type backlight unit of the related art included in an LCD device increases the distance between the light sources and a diffusion plate disposed above the light sources. The direct type backlight unit of the related art can realize uniform brightness, though it decreases brightness and prevents slimness of the LCD device.
Alternatively, another direct type backlight unit of the related art is configured to employ a diffusion plate including diffusion beads, in order to realize both uniform brightness and slimness of the LCD device. The diffusion plate including diffusion beads largely increases the costs the LCD device. Also, the diffusion plate including the beads causes the transmission and reflection of light to be repeated due to a refractive index difference. Accordingly, brightness in the front direction is deteriorated.